Xenon-133, 127Xe, and 125Xe for lung function investigations: a dosimetric comparison.

Of the possible radionuclides of xenon, 127Xe and 125 Xe have better physical properties for lung function measurement than 133Xe. A comparison of the radiation doses for these three radionuclides has been made for a typical scintillation camera investigation. Using an exponential model for washin and washout of gas, it is shown that the specific activity-time relationship is always equal to the product of the spirometer concentration and the rebreathing period. It is concluded that of the three radionuclides 127Xe gives the lowest radiation dose during a typical lung function study.

In vivo assessment of hepatic-arterial and portal-venous components of liver perfusion: concise communication.

An in vivo technique for assessment of the relative contributions of hepatic artery and portal vein to liver perfusion has been developed in the rat. Dynamic scintigrams have been obtained following i.v. bolus injection of Tc-99m sulfur colloid. Temporal separation of the arterial and venous phases has been verified by hepatic-arterial ligation and portacaval diversion. The former procedure abolishes the early arterial phase of normal uptake. Portacaval diversion similarly eliminates the delayed venous phase. Assessment of the individual components of liver perfusion is of promise in the investigation of hepatic dysfunction.

Dynamic spatial resolution.

The study of the dynamic behaviour of radiopharmaceuticals within a patient using a scintillation camera with data acquisition and processing facilities often presents analytical problems because of the limited data available. In the effort to maintain good spatial resolution sensitivity is often needlessly reduced producing further limitation in the statistical accuracy within regions of interest. It is shown that for a particular dynamic study and scintillation camera combination an optimum design of collimator exists, often of much greater sensitivity and poorer resolution than those used hitherto. A simple method is given for producing data for any system which will provide the basic information necessary to read off optimal collimator design parameters.

A simple method for correcting left ventricular equilibrium radionuclide angiography for the effects of arrhythmias.

A simple method of correcting equilibrium radionuclide angiographic data for the effects of arrhythmias is proposed. This involves no further acquisition time or inconvenience to the patient. This correction is necessary in patients with marked arrhythmias as the left ventricular time-activity curve (LVTAC) becomes distorted with greater sampling time in the first few frames of the LVTAC than in later frames. This will show on the LVTAC as greater counts in the first few frames and will lead to an overestimation of left ventricular ejection fraction (LVEF) and wall motion. The method proposed normalises each frame to make the contribution from a non-cardiac region constant over the cardiac cycle. Results of the correction are presented and discussed.

Deconvolution analysis of the scintillation camera renogram.

A scintillation camera with digital data store has been used to assess renal function. Analysis of the renogram by deconvolution, using an on-line digital computer, shows promise as a means of expressing renal function in terms of tubular transit times for 123I-Hippuran.

Assessment of progression of secondary bone lesions following cancer of the breast or prostate using serial radionuclide imaging.

A serial study on 32 patients with bone metastases following cancer of the breast or prostate was performed over three years. Up to ten sets of images (average of four) per patient were obtained during this period using 99Tcm methylene diphosphonate as the radiopharmaceutical. Ninety-three paired serial images of individual lesions were qualitatively assessed for change by three physicians in nuclear medicine and the results were compared with the quantitative results from computer analysis. The reproducibility of the quantitative approach was determined by the analysis of 20 paired lesions by three physicists. It was found that quantitative changes in uptake of less than 20% between images were generally not detected by the medical observers; a change of 41% had only a 95% probability of being identified as change by the physicians. Although much more reproducible in determining changes in individual lesions, the quantitative approach was found to be inferior to the qualitative assessment of overall change in the majority of cases which involve multiple lesions. The basic assumption that uptake varies proportionally with progression of the bone lesion is discussed an is considered in some instances to be untenable. The conclusion is drawn that the determination of progression from changes of uptake in longstanding lesions is uncertain and is subsidiary in importance to the detection of new lesions.

Radionuclide evaluation of valvular regurgitation.

A non-invasive nuclear medicine technique for the assessment of aortic and mitral regurgitation may be of importance in the management of patients with valvular disease. Rigo et al (1979) introduced a method based on measuring the ratio of the left ventricular stroke volume to the right ventricular stroke volume from radionuclide equilibrium gated blood-pool images of the heart. In this paper we report our results using this technique. They indicate that caution should be exercised, and in particular that methods used to define the ventricular regions of interest must be carefully examined.

The effect of various background protocols on the measurement of left ventricular ejection fraction in equilibrium radionuclide angiography.

Four methods of calculating left ventricular ejection fraction from equilibrium radionuclide angiography have been assessed for inter-observer variability and compared to single-plane contrast cineangiography. The superiority of data-processing methods which use a left ventricular region of interest which follows the changing size of the left ventricle into systole is demonstrated. A simple method of correcting for background is suggested as an alternative for those centres not possessing the necessary software for methods involving a changing region of interest.

Prediction of late ischaemic complications after cerebral aneurysm surgery--use of a mobile microcomputer system for the measurement of pre-, intra- and postoperative cerebral blood flow.

Patients with defective autoregulation of cerebral blood flow are at much greater risk of developing late cerebral ischaemia after intracranial aneurysm surgery. This finding was based on data derived from the intraoperative measurement of the response of the cerebral circulation to hypotension, deliberately induced to assist dissection and clipping of the aneurysm. A preoperative test which gave the same information as the intraoperative measurements might be helpful in predicting the optimal timing of aneurysm surgery. However, the original intraoperative intravenous 133Xenon injection method was limited both by the need to analyse the data off-line and the restricted number of runs (up to 6). This paper describes the modifications used, based on the Apple II microprocessor, to obtain values of cerebral blood flow within 6 minutes of the injection of 133Xenon with up to 15-20 runs per patient.

Detection and interaction of elastic and flow-resistive respiratory loads in man.

1. The detection of added inspiratory airflow resistances was studied in normal individuals under two circumstances: first, while breathing unhindered, and secondly, while breathing against continuously applied ('basal') inspiratory elastic loads. The addition of basal elastic loads resulted in impaired detection of flow-resistive loads whether expressed as added flow resistance or as a proportion of the basal flow resistance. 2. When loads were plotted on a logarithmic scale, load-detection relationships were linear, permitting both threshold and slope of the detection response ('sensitivity') to be assessed. Impaired detection associated with basal elastic loads was shown to be due to a raised threshold without change in 'sensitivity'. 3. When the flow resistances submitted for detection were expressed as a proportion of the sum of the basal flow resistance and added elastance, the probability of detection was independent of the magnitude of the added elastance. 4. The interaction between basal elastic and added flow-resistive loads suggests that at the time of detection the basal elastance acts in a manner similar to that of an added flow resistance. 5. Added basal flow resistances had no significant effect on the detection of threshold elastic loads.